A Spectroscopic Study of Dioxygen Reactivity with Non-Heme Metal Centers The goal of this project is to enhance the current understanding of the chemistry involved in the reactions of dioxygen (O2) with the non-heme bimettalic centers of hemerythrin and hemocyanin, two of the three known dioxygen-carrier proteins, using methods of time-resolved laser spectroscopy. Specifically femtosecond pump-probe, laser photolysis, time-resolved circular dichroism, and photoacoustic calorimetry experiments will be conduct to probe interactions between the metal centers and the active site environments of the target systems. It is our goal to determine the effect of protein structure and solvent conditions on the mechanism and rate of dioxygen binding and release. These experimental results will increase our limited understanding of how protein active site structure and composition control biologically relevant dioxygen binding reactions. In addition, these studies will have clinical impact in an important area: they will provide information on how non- heme metal centers reversibly bind dioxygen, and may facilitate the develop of new, more efficient, dioxygen carriers for blood substitutes.